Tire pressure monitoring system transmission protocol

ABSTRACT

A system for monitoring conditions within a tire includes a sensor assemblies ( 14 ). The sensor assemblies ( 14 ) emit a transmission ( 26 ) containing information indicative of conditions within a tire to a receiver ( 16 ). The transmission ( 26 ) from the sensor assemblies ( 14 ) includes an amplitude shift key wake up portion and various data packet portions. The data packet portions are separated by a variable interval to prevent collisions of transmissions at the receiver.

CROSS REFERENCE TO RELATED APPLICATION

The present invention is a continuation of U.S. patent application Ser.No. 10/298,058, filed Nov. 15, 2002, which claims priority to U.S.Provisional Patent Application Ser. No. 60/336,265 filed Nov. 15, 2001.

BACKGROUND OF THE INVENTION

This invention relates to a system for monitoring conditions within atire, and specifically to a transmission signal protocol for informationtransmitted from a tire pressure-monitoring sensor within the tire.

Current government regulations have established that tire pressure mustbe monitored to provide a vehicle operator with information warning ofimproper tire conditions. Notification of tire conditions aids inmaintaining optimal tire operating parameters that in turn improvessafety and handling of the motor vehicle. Further, monitoring ofconditions within a tire allows the operator to maintain tire pressurewithin an optimal range, to optimize fuel economy, vehicle handling,performance and safety.

Conventional methods of monitoring tire pressure include positioning asensor assembly within each wheel to monitor pressure, temperature andother conditions effecting tire performance. The sensor assembliesdisposed within each tire gather transmit a radio frequency transmissioncontaining data indicative of tire conditions. The transmission isreceived by a receiver disposed within the vehicle that providesinformation to a controller. The tire pressure data transmitted to thereceiver is then displayed to the driver with information required towarn of improper conditions or to provide specific numerical data forconditions within the tire.

The sensor assemblies disposed within each of the tires are operated bya battery. Because the battery is disposed within the tire and access tothe battery requires removal of the tire, it is desirable to reduce andminimize the power required to operate this sensor and transmit the datasignal to the receiver. It is desirable to develop a system and protocolfor transmitting the signal and data to the receiver depending onvarious conditions of the vehicle to prolong battery life.

Accordingly, it is desirable to develop a transmission protocol for thetire pressure monitoring system that extends battery life bytransmitting data indicative of tire conditions to a receiver accordingto specific vehicle operating parameters.

SUMMARY OF THE INVENTION

An embodiment of this invention is a transmission protocol for a tirepressure monitoring system transmitted from a sensor disposed withineach of the tires that senses conditions indicative of tire pressure andtemperature.

The transmitter disposed within the tire receives data from the sensorwithin the tire and transmits that data to a receiver according to adesired transmission protocol. The data transmission protocol includes apreamble portion. The preamble portion includes an Amplitude Shift Keyed(ASK) wakeup signal. The data portion of the transmission is a FrequencyShift Keyed (FSK) signal. The ASK wakeup signal signals the receiver andindicates that the data portion of the transmission will follow.

The receiver is initial configured to receive ASK signals. Eachtransmission from the tire pressure monitoring sensor assembly includesthe preamble portion and ASK signal that triggers the receiver to switchto receive FSK mode. In the FSK mode, the data packet portionscontaining data indicative of tire conditions is received by thereceiver.

The transmission from the sensors includes data indicative of tirepressure; tire temperature and other conditions within the tire.Further, data transmitted by the sensor assembly includes various checksto ensure and check operation of the sensor assembly.

The transmission protocol for the tire pressure monitoring system ofthis invention conserves battery power and efficiently providesinformation indicative of conditions within a tire according to specificvehicle operating conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1 is a schematic view of a motor vehicle including a tiremonitoring and remote keyless entry system;

FIG. 2 is a schematic view of the elements comprising a transmissionfrom the tire sensor assembly;

FIG. 3 is a schematic view of the transmission signal including variableintervals;

FIG. 4 is schematic illustration of data transmissions transmitted atvariable intervals;

FIG. 5 is a schematic illustration of a transmission signal includinginformation indicative of tire conditions; and

FIG. 6 is a schematic illustration of a receiver assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an embodiment of this invention is a system formonitoring conditions within tires 12, mounted to a motor vehicle 10. Amotor vehicle 10 includes at least four tires 12, each including asensor assembly 14. In some instances, a spare tire 11 also includes asensor assembly 14 to eliminate the need for exchanging sensorassemblies 14 for a deflated tire. The spare tire 11 also include asensor assembly 14 in order to provide the required data tire conditionsfor the spare tire 11 during its use as a replacement for one of theother tires 12. Further, the sensor assembly 14 within the spare tire 11transmits information indicative of tire conditions at least once a day,or anytime pressure goes low. The sensor assemblies 14 disposed withineach of the tires 12, 11 may be of any type known to a worker skilled inthe art. Typically, the sensor assemblies 14 are installed as a portionof an air inlet valve to each of the tires 12, 11 and include a sensorassembly to sense temperature and pressure within each of the tires 12,11. Each of the sensor assemblies 14 is powered by a battery andtransmits signals to a receiver 16 indicative of condition with thetires 12, 11 according to a specific protocol to extend battery life.

The tire pressure monitoring system includes a receiver 16 that receivessignals from the sensor assemblies 14 within the tires 12, 11 andforwards that information to a micro-controller 25. The micro-controller25 then sends the signal to a display 18 to communicate information tothe operator. The receiver 16 may also receive a signal from a key fob22 to activate a remote keyless entry system 20. The remote keylessentry system 20 controls locks on doors 24 or may also be used to engageother functions of the motor vehicle 10. As appreciated, operation of aremote keyless entry system 20 is as known to a worker skilled in theart and may operate many other functions of the motor vehicle 10.

Referring to FIG. 2, the components of a transmission signal 26 isschematically illustrated. Transmission signal 26 emitted from the tiresensor 14 includes a transmission preamble portion 28, followed by datapacket portions 31. The transmission signal 26 from the tire pressuresensor 14 is transmitted to the receiver 16. Each of these portionsincludes specific information indicative of conditions within thecorresponding tire 12, 11.

Referring to FIG. 3, the transmission preamble portion 28 includes anamplitude shift key (ASK) wakeup signal 29. The ASK signal 29 initiatesthe receiver 16 to change over from ASK mode to FSK mode. The ASK modeis the mode that is used for the remote keyless entry system 20. The ASKmode is most desirable for transmissions that require high power and notsubject to variations in distance between the receiver 16 and thetransmitter 22. Further, the ASK signal 29 is best suited fortransmissions where the transmitter and receiver are essentiallystationary relative to each other.

The ASK signal 29 is composed a plurality of data packets 27 of aspecific pattern. Preferably, there are twelve identical packets 27,each including five bytes. The first two bytes, indicated at 30, are ofa data value of “0”. The remaining bits, indicated at 33 are off. Eachpacket is 4.16 ms long. The specific pattern is selected to minimize theduty cycle of the wakeup pattern to allow the highest averaging factorpossible in view of local restrictions.

Each data transmission 26 includes a number of data packets 31 separatedby a variable interval 58. Each data packet 31 contains ninety-six bitstransmitted in FSK format that is 10 ms in duration. The variableinterval 58 separating the data packets 31 reduces and substantiallyeliminates the probability that transmissions 26 from other sensorassemblies 14 will overlap at the receiver 16. The receipt of two ormore data packets 31 simultaneously overlapped is known as a datacollision. The receiver 16 will not recognize transmissions 26 collidedor overlapped because the overlapped data frames are of a greaterduration than the receiver 16 is programmed to receive. Overlapping dataframes 31 causes a receiver 16 to ignore the data frames 31. Repeateddata collisions will eliminate data from at least two of the data sensorassemblies 14.

Referring to FIG. 4, each data signal 26 includes a duration 68. Betweeneach data signal is an interval 64. The interval 64 is of a fixedduration than the data transmission 26 would be repeated and result in atransmission 66 of increased duration. As appreciated, when the receiver16 receives a transmission of increased duration 66 it will simplyignore it because it is of a different length than that than which thereceiver 16 is programmed to receive. The receiver 16 is programmed toreceive signals of certain duration in order to ensure that the receiver16 is actually receiving information from tire pressure monitoringassemblies 14 disposed on that vehicle. Further, the receiver 16 alsoonly responds to signals of a certain duration in order to preventinterference and confusion that may be caused by overlapping signals.

Referring to FIG. 3, the system of this invention includes a method ofpreventing repeated data collision. The sensor assemblies 14 of thisinvention prevent overlapping data frames 31 by varying thepredetermined intervals 58 between the data packets 31 in a randommanner. The length of the data frame 31 is preferably 10 millisecondswith the interval 58 varying according to the below equation.Interval length=standard length+(beta*standard length)

Where: interval length is the length of time in ms between data frames;

-   -   i. Standard length is a predetermined duration of time in ms;        and    -   ii. Beta is a random variable with a value between 0 and 1.

Preferably, the standard length of time is 100 milliseconds; therefore,the interval length will vary between 100 milliseconds and 200milliseconds depending on the value of beta. Each transmission 26 fromthe sensor assemblies 14 are set with differing variable intervals 58,such that even if one or more data packets 31 overlap for any onetransmission, subsequent data packets 31 will not overlap therebypreventing cyclical or repeated overlap. As appreciated differinglengths of data, frames are within the contemplation of this inventionand a worker skilled in the art would recognize the application of thismethod to other lengths of data transmissions.

In another embodiment of this invention, the length of the variableinterval 58 is transmitted to the receiver assembly 16. The receiverassembly 16 will then expect the next data packet 31 at the communicatedinterval. This allows a receiver assembly 16 to switch back to the ASKreceiver between data frames 31. This is known in the art asinterleaving and is preferable in systems using a remote keyless entrysystem and a tire pressure monitoring system that share a commonreceiver. In this way, the common receiver can receive remote keylessentry signal data and tire pressure-monitoring data without creatingperiods of blackouts for either system.

Another factor considered in preventing signal collision is thetransmission rate. The faster a rate the data is transmitted to thereceiver the lower the probability of data collision. Preferably, thesystem of this invention includes a rate of 9.6 killibauds. However, aworker skilled in the art would understand that different datatransmission rates are within the contemplation of this invention aswould be required by specific regulations in specific areas.

Referring to FIG. 5, each data packet 31 includes a data packet preambleportion 34, an identification portion 38 and the data portion 32. Eachof those portions is divided into specific elements having specificpurposes relevant to the transmission 26. The preamble portion 29includes the fifteen bits containing “zero” bits terminated by a startbit 36 with a value of Data “one.

The identification portion 38 includes thirty-two identification bits.The identification bits include various data including productidentification and other information that would indicate the position ofthe sensor on the specific vehicle relating to the receiver 16. Theidentification bits provide information on the specific product serialnumber and identification information used by the receiver 16 todifferentiate tire pressure monitoring transmissions emitted from thevehicle from other vehicles that may be in the same proximity to thereceiver 16.

A data portion indicated at 32 includes pressure information,temperature information, status information and other information thatrelays the present condition of the sensor assembly 14. The pressureinformation indicated at 40 includes eight bits that indicate pressurewithin the tire 12, 11. The eight bits are calibrated to a specific zeropressure and indicate any deviation from that zero pressure. Preferably,the zero pressure is 14.7 pounds per square inch (PSI). Changes fromthis zero pressure are indicated by the ten bits that make up thepressure data portion of the data portion indicated at 32 and willregister changes in pressure from zero pressure in 0.11-PSI increments.The maximum pressure that the pressure bits will indicate is 12,115 PSI.

A next data portion indicated at 42 includes information indicative oftemperature within the tires 12, 11. The temperature and data portionincludes eight bits. The eight bits include a specific value indicativeof change from a zero point. Preferably, the zero point in this systemis −40° C. and changes in 1° C. increments from the zero point areindicated by the values of the eight bits and the temperature portion ofthe data packets 42.

A next data portion indicated at 44 includes eight bits providing anindication of acceleration. The eight bits indicated at 44 definesacceleration. Another bit includes information on the status the batteryand is indicated at 46. A “0” value indicates that the battery is at anormal level and a value of “1” indicates that the battery is at a lowlevel.

A frame number bit indicated at 48 provides information as to whatnumber data packet is currently being transmitted. As shown in FIG. 3,there are four data packets for each transmission 26. The frame numberbits 48 simply indicate which data packet is currently beingtransmitted.

Four bits indicated at 50 provide software version information. Thesoftware version information 50 provides information used in programmingthe receiver and also in determining the proper operation of the tirepressure monitoring system. Further, many other uses as is known to aworker skilled in the art are would be communicated by informationindicative of the software version.

Three bits indicated at 52 include information concerning the delay timebetween data packets 31. The time between data packets is calculatedaccording to a specific algorithm and communicated to the receiver 16,in order for the receiver 16 to expect further transmission of the datafrom specific sensor and predetermined time based on the variableinterval 58.

The wake up status bit section provides a code indicated at 53. The codebits transmit information and are arranged to transmit and provideinformation to the receiver 16 that the sensor assembly 14 is in a learnmode, normal mode, over temperature mode, wake mode or a forcedtransmission mode. Further, the wake up status information bits 53 canbe used for other purposes and to indicate other modes of operation ofthe sensor assembly. The learn mode is indicated by all of the bitshaving a value of “1111”. A learn mode is when the sensor assembly 14 istriggered to transmitting identification code indicative of the specificsensor to a receiver in order for the receiver to learn the specificlocation of the sensor assembly on the motor vehicle.

In a normal mode, the sensor assembly is operating under normalconditions to send transmissions indicative of tire conditions to thereceiver at the predetermined intervals. The normal mode is indicated bythe four bits including a value of “0001”.

The over temp mode indicates a condition where the temperature hasincreased over a predetermined and pre-selected temperature. The overtemp mode is indicated by a bit value of “0010”.

The wake function code indicates that the sensor assembly is nowrotating and has moved from a parked condition to an operatingcondition. This wake function code bit has a value of “0011”. The wakeis used to indicate and detect whether the vehicle is parked or inoperation.

The forced transmission bit is indicated by a value of “0100”. Theforced transmission function code indicates that the sensor assembly hasbeen externally activated to transmit data indicative of tireconditions. Sensor assemblies are externally triggered to transmit dataindicative of tire conditions when it is desired to teach the receiverthe position of each of the sensor assemblies. In other words, a magnetor other device may be used to trigger transmission of a data signalfrom a specific sensor 14 in order for the receiver to learn whichsensor belong to that vehicle and at what location such as left front,right front or other position on the vehicle that the sensor is located.

In a normal mode, the sensor assembly is operating under normalconditions to send transmissions indicative of tire conditions to thereceiver at the predetermined intervals. The normal mode is indicated bythe five bits including a value of “0001”.

The check sum information indicated at 54 includes eight bits that arearranged to represent the sum of all of the bits. Check sum includes allof the bits except for the preamble bits. This includes a bit stream of58 bits. When the stream of bits is split into pairs of bits, itincludes a series of zeros and ones that can be converted to a decimalequivalent. Each pair is converted to a decimal equivalent and then eachpair is added to all of the other pairs. The sum of all the decimalvalues is then indicated in binary form at the check sum bit. Thisbinary form acts as a check of the data signal to the receiver to ensurethat all of the data bits have been received and that the receiver hasin fact received a complete signal. Check sum data bit will change asvalues of the data packets and other function signals within thetransmission change.

The final bit is indicated at 56 as a stop bit. This signifies that thedata packet transmission by sending a Manchester data “0” followed byone bit time high. The Manchester data “0” is part of the Manchestercode. The Manchester code, known by workers skilled in the art is acoding in which data and clock signals are combined to form a singleself-synchronizing data string. Each included bit contains atransmission at the mid-point of a bit. The direction of the transitiondetermines whether a bit is a “0” or a “1”. In the first half is a truebit value and the second half is the complement of the true bit value.The stop bit signifies the end of the data packet transmission from thisspecific transmission.

Referring to FIG. 6, the receiver assembly 16 includes an ASK portion 74and an FSK portion 72. The receiver assembly 16 also includes an antenna78 to receive transmissions from the key fob 22 and the sensorassemblies 14. The antenna 78 is preferably of a length one quarter thatof the wavelength of the transmission received. Transmissions receivedby the antenna 78 proceed through a resistor 80 to the RF receiver 16. Acontroller 76 controls whether the ASK portion 74 or the FSK portion 72is engaged to receive incoming transmissions.

The receiver 16 defaults to sending transmissions to the ASK portion 74of the receiver 16. The ASK portion 74 operates at a low power and istherefore the default when the receiver 16 is activated. The ASK portion74 is engaged while the motor vehicle 10 is stopped or parked.Preferably, the ASK receiver 74 is engaged in response to the speed ofthe motor vehicle 10 being below a predetermined speed. Thepredetermined speed is preferably below 10 miles an hour. Above 10miles, an hour the receiver assembly 16 will change over to the FSKportion 72. That is, that any signals received by the receiver 16 atthat time will be automatically directed to the FSK portion 72 of thereceiver. The FSK portion 72 will then receive transmissions from thesensor assemblies 14 disposed within each of the tires 12, 11.

The conditions of the motor vehicle 10, whether it is traveling at thedesired speed or is parked, provide definite indicators on whether theFSK portion 72 or the ASK portion 74 are the default receiver forincoming transmissions. However, when the vehicle 10 is idling, forinstance in a traffic jam, but not moving at a speed causing switch overto FSK portion 72 the system will not switch over to the FSK portion 72unless another condition is satisfied. Each transmission includes theASK wake up signal 28 that is sent before the FSK data packets 31 (FIG.2) transmission. The ASK wake up signal 28 alerts the receiver assembly16 to the incoming FSK transmission which causes the receiver assembly16 to switch over to the FSK portion 72. The switchover allows thereceiver assembly 16 to accept data indicative of tire condition fromthe sensor assemblies 14 while the automobile is parked or idling intraffic.

Preferably, each of the sensor assemblies 14 will transmit signalsindicative of tire conditions at differing rates depending on the speedof the motor vehicle. At speeds above a predetermined speed the sensorassembly will transmit the tire condition data at a greater frequency.At lower speeds indicative of a parked vehicle, the sensor assemblies 14transmit at a lower rate. Preferably, the predetermined speed is 10miles an hour and the sensor assemblies 14 will transmit signalsindicative of tire conditions once every minute. Below the ten miles perhour predetermined speed threshold, the sensor assemblies 14 willtransmit the signals only after sensing a change in tire pressure abovea desired amount indicative of a tire losing air pressure. Once aninitial loss of pressure is sensed, the sensor assemblies 14 aretriggered to transmit signals at one-minute intervals.

Although specific speeds and intervals of data transmission arediscussed, a worker knowledgeable in the art would understand that it iswithin the contemplation of this invention to use the other speeds anddata transmissions and rules according to specific application criteria.The selective actuation of each sensor assembly 14 and switching betweenASK portion 74 and FSK portions 72 of the receiver 16 prevents signalcollisions between ASK and FSK transmission emitted by the remotekeyless entry system 20 and signals form the sensors 14 to optimizefunction of the receiver assembly 16.

The foregoing description is exemplary and not just a materialspecification. The invention has been described in an illustrativemanner, and should be understood that the terminology used is intendedto be in the nature of words of description rather than of limitation.Many modifications and variations of the present invention are possiblein light of the above teachings. The preferred embodiments of thisinvention have been disclosed, however, one of ordinary skill in the artwould recognize that certain modifications are within the scope of thisinvention. It is understood that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed. For that reason the following claims should be studied todetermine the true scope and content of this invention.

1. A method of transmitting information indicative of conditions withina tire comprising the steps of: a. transmitting a signal including anamplitude shift keyed transmission preamble to a receiver; b.transmitting a frequency shift keyed (FSK) identification code from afirst transmitter; c. transmitting a fsk signal indicative of pressurewithin the tire from the first transmitter; d. transmitting a fsk signalindicative of temperature within the tire from the first transmitter, e.varying a time interval between portions of said identification code,said signal indicative of pressure within the tire, and said signalindicative of temperature within the tire; and f. receiving one of afrequency shift keyed (FSK) identification code, an FSK signalindicative of pressure within a tire, and an FSK signal indicative of atemperature within a tire from a second transmitter within the timeinterval between portions of any of the FSK signals from the firsttransmitter.
 2. The method of claim 1, wherein said step of varying saidtime interval includes transmitting a length of the interval to areceiver such that the receiver prepares to receive a next data packetat the communicated time interval.
 3. The method of claim 2, whereinsaid time interval varies in response to vehicle operating parameters.4. The method of claim 3, wherein said operating parameter includesvehicle speed, and a frequency of said transmissions are increased inresponse to an indication of pressure loss at a pre-selected rate. 5.The method of claim 4, wherein said frequency of said transmissions aredecreased in response to a vehicle not moving for a set period.
 6. Themethod of claim 5, wherein said frequency of said transmissions variesaccording to vehicle speed.